With the development of display techniques, the world is demanding more and more on the vision effect as well as the portability of display devices. On one hand, wider view angle and three-dimensional display effect are needed; on the other hand, people want to make the display device itself as small as possible for easy use. To satisfy these two demands, which normally conflict, at present, various available display technologies have been developed. The display techniques of concern are generally divided two categories, i.e. head-mounted and non-head-mounted, and their disadvantages are listed below:
categorydisplay technologydisadvantagesnon-head-parallax barrierViewers are confined on specific view angles;mountedShort range eye focusing conflicts with the convergence angle,which causes visual fatigue.Small view angle, poor telepresence vision.Large screen, poor portability.holographyThe image reproducing condition is hard to meet and not widelyapplicable.Due to the lack of proper recording medium, dynamic display ofimages is still difficult.Despite of the vivid image, the narrow view angle limits thetelepresency.Complex devices, poor portability.head-shutter glasses/Large screen, poor portability.mountedcomplementary colorShort range eye focusing conflicts with the convergence angle,glasses/which causes visual fatigue.Polaroid glassesSmall view angle, poor telepresence vision.Helmet mounted displayBig, heavy and energy consuming devices, poor portability.(HMD) methodView angle limited by the optical lens aperture, poortelepresence vision.Short range eye focusing conflicts with the convergence angle,which causes visual fatigue.
In brief, the aforementioned various display devices and display methods all suffer from narrow view angles, lack of telepresence vision and poor portability. Moreover, most of the display technologies listed above, except for holography, will cause visual fatigue.
The common feature of the existing display technologies is that a real or virtual image is established somewhere in the space, then the human eyes actively focus and look at that real or virtual image in the specific position, thereby forming the vision.